http://unisci.com/stories/19994/1117991.htm
"Any large disturbance in air -- a lightning bolt or a high-speed train
entering a tunnel -- normally generates a traveling sound wave that changes
shape as it propagates. If the pulse doesn't dissipate first, it eventually
forms a shock wave. (In the case of lightning, the thunderclap forms
immediately.)
Solitary waves in optical fibers maintain their shape because the material
exhibits "dispersion," a speed of light that depends on frequency in just
the right way. But the speed of sound in air is relatively independent of
frequency, so solitary sound waves have remained a great challenge.
Communications engineers want complex light signals to travel through long
fiberoptic cables without changing shape, which is why they've been
developing optical solitary waves -- waveforms that travel long distances
without distortion.
But solitary sound waves have been thought to be very difficult to produce
because the properties of air don't seem to permit them.
In Monday's Physical Review Letters, a Japanese team demonstrates the first
production of acoustic solitary waves in air, which they say could lead to
the undistorted transmission of heat and other forms of energy, as well as
the elimination of troublesome shock waves from train tunnels and air
compressors".
ttyl
-Steve
steve@primeline.net | ICQ: 5113616
Digital Fusion: http://www.digitalfusion.on.ca
Fiero Project: http://www.digitalfusion.on.ca/fiero
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